1. Field of the Invention
This invention pertains to wall construction and more particularly to wall construction that provides heat retention for interior purposes while accommodating to the exterior environment in an energy-saving manner.
2. Description of the Prior Art
Wall construction for residential and commercial buildings is varied and usually comprise a plurality of layers of load or non-load supporting materials, heat insulation, and moisture proofing materials. Actual heat flow through a wall section, under real conditions, involves many variables, but the primary factor used for steady-state calculations is the calculated thermal conductance, or U value, for the wall. In effect, the U value is a measure of heat loss, usually expressed in terms of BTU per hour per square foot of surface. The reciprocal of thermal conductance is thermal resistance, its units being typically Fahrenheit degrees per BTU per hour per square foot. Thus, a wall with a U value of 0.25 would have a resistance value of 1/U=1/0.25=4.
But the U value or thermal resistance value does not tell the whole story concerning heat loss. The factor of time lag is an important ingredient since it is a measure of the thermal inertia of the wall system. Time lag is the delay caused by heat storage and its subsequent release (usually by radiation) by the structure. In many respects, and building types, the time lag factor is the more important of the two factors since it is a measure of how quickly the interior face or surface of a wall at a steady-state temperature changes when the exterior surface or face is exposed to a different temperature. Therefore, the combined factors of U value and time lag are important in determining the heat retention efficiency of a wall structure. Heat retention is directly dependent on the non-insulated mass of the system. The greater the mass, the greater the heat retention.
It is possible using conventional construction techniques to increase the heat retention value of a wall, but to do so usually requires increasing the mass of the wall. To increase the mass generally means to increase the cost of construction. Furthermore, increasing the heat retention value of a wall is not totally beneficial to energy conservation, since a heat retaining structure has thermal inertia requiring, for instance, internally air conditioning a room after dark in the summer time when the sun has gone down and the environmental outside temperature has cooled down considerably.
Many wall systems comprise three basic elements: the interior mass, the core insulation, and the exterior mass. Assuming that the interior mass is at a steady-state condition of 70.degree. F. and the exterior mass is at a steady-state condition of 100.degree. F., as exposed to the environment of a hot summer day. When the sun goes down and the environment reduces to 80.degree. F., the interior mass is still exposed to the much higher temperature of the retained heat being radiated from the exterior mass. Hence, the air conditioning system cooling the interior area next to the interior mass continues to run at a cooling level not indicative of the outside environment. The reverse occurs in cold climates where the mass retains the exterior cold temperature.
In addition to the absolute temperature value of a room, comfort of an individual within the room is dependent on another phenomenon. If the nearby wall where the individual is positioned is much colder or warmer than the environment within the room, the individual will be uncomfortable because of the phenomenon of relative radiation. That is, if the wall is at a high temperature, the wall will be as a heat radiator and will not be comfortable to stand before, whereas if the wall is cold, it will act as a temperature absorber, drawing heat away from the body of the individual, even giving the sensation of a draft.
Therefore, it is a feature of the present invention to provide an improved wall system so that the environment within the interior area adjacent the wall system is retained for a much longer period of time when compared with the period of time for an equally insulated wall system of conventional construction having the same U value by increasing the time lag thereof, thereby increasing the efficiency of the air conditioning and heating systems for the interior area.
It is another feature of the present invention to provide an improved wall system for minimizing wide temperature variations to which the interior face of the system is subjected, thereby greatly increasing the comfort of individuals within the room bounded by the wall by stabilizing the wall-radiation conditions, while also minimizing extreme temperature exposures of the wall mass, thereby achieving substantially constant maintenance effort and cost by reducing thermal expansion and contraction.